Lawson cypress Toxic?

Updated 2026-03-06| 5 min read| 3,477 found this helpful

All parts of Lawson cypress are toxic, containing harmful compounds including thujone, tropolone and picric acid

Exposure (primarily ingestion) leads to gastrointestinal irritation and symptoms of gastroenteritis in humans

Treatment focuses on decontamination and symptomatic management of observed adverse effects

FAQ

Is Lawson cypress toxic to Humans?

Gastroenteritis, including abdominal pain, nausea, vomiting and diarrhea (Moderate)

Is Lawson cypress toxic to Cats?

Formal toxicity data is not documented; ingestion may cause gastrointestinal distress similar to human reactions (Unknown)

Is Lawson cypress toxic to Dogs?

Formal toxicity data is not documented; ingestion may cause gastrointestinal distress similar to human reactions (Unknown)

Is Lawson cypress toxic to Horses?

Formal toxicity data is not documented; ingestion may cause gastrointestinal distress similar to human reactions (Unknown)

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Toxicity Details

Humans

Moderate

Gastroenteritis, including abdominal pain, nausea, vomiting and diarrhea

Cats

Unknown

Formal toxicity data is not documented; ingestion may cause gastrointestinal distress similar to human reactions

Dogs

Unknown

Formal toxicity data is not documented; ingestion may cause gastrointestinal distress similar to human reactions

Horses

Unknown

Formal toxicity data is not documented; ingestion may cause gastrointestinal distress similar to human reactions

Toxicity Snapshot

Toxic PartsAll plant parts

Exposure RoutePrimary exposure route is ingestion of plant material; skin contact with sap may cause mild localized irritation

Toxic CompoundsMonoterpene thujone; Tropolone; Picric acid (lignin derivative)

First Aid & Prevention

First 30 Minutes

• If ingested, rinse mouth thoroughly with clean water to remove remaining plant residue
• If skin contact occurs, wash affected area with mild soap and running water for 10-15 minutes
• Do not induce vomiting unless explicitly instructed by a medical professional or poison control

Contact Vet Immediately

• Persistent vomiting, diarrhea or abdominal pain develops after exposure
• Large quantities of plant material have been ingested
• Severe distress, swelling or allergic reaction is observed post-exposure

Prevention

• Keep the plant out of reach of children, pets and livestock that may chew on foliage
• Wear protective gloves when handling the plant to avoid contact with toxic sap and compounds
• Clearly label the plant if grown in accessible areas to prevent accidental ingestion

Treatment & Prognosis

• Decontamination of exposed skin or digestive tract as appropriate
• Symptomatic treatment for gastrointestinal distress (e.g. anti-emetics, fluid replacement for dehydration)
• Monitoring of vital signs and symptoms for 24 to 48 hours post-exposure

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Professional Toxicology

Scientific NameChamaecyparis lawsoniana (A.Murray bis) Parl.

AliasesPort Orford cedar

Toxicity Grade

HumansModerate

CatsUnknown

DogsUnknown

HorsesUnknown

Target Organs

Gastrointestinal tract

Mechanism of Action

• Toxic compounds irritate the mucosal lining of the gastrointestinal tract, triggering inflammatory reactions that cause gastroenteritis symptoms

Other Species Risk (CliniTox)

Information from CliniTox veterinary text.

Cattle: No formal toxicity data available; ingestion of large amounts may cause gastrointestinal irritation

Sheep: No formal toxicity records on file; reactions similar to other conifer poisoning are expected if ingested

Small companion mammals (rabbits, guinea pigs, hamsters): Ingestion may lead to digestive upset and systemic toxic reactions; access to the plant should be strictly avoided

Confusion Risk

The following plants look similar and may be confused:

Other false cypress species Chamaecyparis spp.

Morphologically nearly identical to Lawson cypress; many species have comparable or higher toxicity levels

American arborvitae (northern white cedar) Thuja occidentalis

Visually similar evergreen conifer in the Cupressaceae family; confirmed to be severely toxic

Mediterranean cypress Cupressus sempervirens

Similar needle-like evergreen foliage; confirmed to be highly toxic

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Related Toxic Plants

American arborvitae

Thuja occidentalis

Severely toxic

Mediterranean cypress

Cupressus sempervirens

Highly toxic

Eastern red cedar

Juniperus virginiana

Moderately toxic

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Data Sources

1. CliniTox (Universität Zürich)

This information is for reference only and does not constitute medical advice. If ingestion or poisoning is suspected, seek medical or veterinary attention immediately.